Control of Stable Flies and House Flies

Stable flies and house flies are major pests near confined livestock facilities, cattle feedlots, and dairies, and cost livestock producers millions of pounds annually.

Losses result from decreased weight gains and production by cattle that suffer the attack of the stable fly. Economic losses due to the house fly are much more difficult to determine, but nevertheless they are a nuisance to livestock and people.

Adult stable and house fly identification and feeding habits

The house fly and the stable fly are very similar in size and appearance. However, they can be easily differentiated by their mouthparts. The stable fly's mouthparts project straight forward from under the head (bayonet type) while the house fly has a sponging sucking type mouthpart. The stable fly also has dark spots on the top of its abdomen (its back).

Their feeding habits and behaviour are quite different. House flies do not bite, but rather sponge up their food from living animals (blood from wounds, saliva, and eye secretions), carcasses of dead animals, or from organic wastes. Such a diet can provide the means to contract and transmit disease organisms. The stable fly ýbitesţ and, in fact, both sexes require a blood meal to reach sexual maturity. The mouthpart is used to lacerate the skin during the biting process. The bite is likened to a combination of jackhammering and sawing.

Numerous animal species serve as hosts but cattle, horses, and dogs seem to be preferred. Laboratory tests have found blood from humans, deer, chickens, rabbits, sheep, and swine in the gut of the stable fly. A stable fly feeds on the tops of the ears of dogs, the front legs of other animals, or on the ankles of humans, feeding until it is engorged. Then it moves to a resting place (usually shade in hot weather) to digest the blood meal.

Stable flies feed from one to three times per day depending on the climatic conditions. Maximum feeding occurs usually about midday. Increased temperature and decreased relative humidity and / or wind with radiation (drying conditions) decreases feeding activity.

Facility management, sanitation, and manure handling

Studies indicate that good sanitation practices are a must to reduce fly breeding areas around feedlots and dairies. House flies may occasionally deposit eggs in fresh manure but they prefer, and stable flies require, a moist manure-and-soil or organic matter and soil mixture 4 inches to a foot deep. This mixture does not get 4 inches deep overnight. It does require the foot action of cattle to mix their manure with the soil. So keeping all lots scraped and cleaned regularly is an extremely important management practice.

Areas behind feeding aprons, around water troughs, potholes, and along fence lines tend to get a lot of foot traffic, catch a lot of manure, and become low, wet areas. Because they are lower than the rest of the lot, these areas tend to catch a large amount of runoff after each rain, making them ideal sites for flies to deposit their eggs. This is why low areas need to be scraped out and filled with fresh dirt regularly.

Other problem areas include drainage areas within pens and channel areas behind pens where water moves to the holding lagoons, spilled feed along feedbunks or wet feed in the feed storage areas, leaky water fountains, drainage along silage piles, the edges of manure storage piles (unless covered with black plastic), sick pen hay or straw bedding, any place where old hay or spilled feed or manure accumulates.

These areas and all pens need to be cleaned completely every spring and at biweekly intervals throughout the summer. Manure should either be spread on the land to dry out or be piled and covered with plastic traps for later disposal.

Chemical control

A number of chemicals and application methods have been used to control stable and house flies while feeding upon host animals, most with limited success. Wet sprays applied to the animal, usually with a mist blower, may reduce stable fly numbers by 75% on day one after treatment, but control will drop to less than 50% by the fourth day and may not be evident by the seventh.

Stable flies prefer to feed on the front legs of cattle. When spraying a group of animals getting a good cover on the legs is very difficult. Cattle also have the habit of walking through water and wet vegetation, which quickly wash off the insecticide.

Dust bags, oilers, and insecticide-impregnated ear tags are even less effective for the control of stable and house flies because these self-treatment devices fail to deposit the required amount of insecticide on the cattle's legs.

Baits may be useful around the office or feedmill but are only effective on house flies and would not be of much help in overall control as fly populations are just too high in the lots.

Oral larvicides that are incorporated into the feed and pass through the animalÝs digestive track and into the manure are also relatively ineffective in controlling stable and house flies. They are of some benefit in more arid regions because house flies will deposit eggs in fresh manure. Stable flies, however, will only lay eggs in moist, non-compacted manure dirt mixtures or spilled feed. The toxic effects of the oral larvicide are lost by the time the manure dirt mixture is suitable for stable fly and most house fly breeding.

When used as part of IPM program, residual insecticides can be very effective on fly resting areas. These insecticides will remain effective for 10 days or longer if not exposed to UV light or washed off with rain. They are useful when applied to sides of buildings or fly resting areas around the office or feed handling facilities. House flies seek shelter at night on inside walls of open buildings or under eaves of the outside buildings. If these areas can be located, residual sprays can be quite effective.

Understanding some of the habits of flies will improve control. It is well known that after stable flies obtain a blood meal they seek a shaded area to digest their meal. Shady sides of buildings, shady sides of windbreaks near the lots, or shady sides of feedbunks may have high numbers of flies resting on them during the hot part of the day. Spraying these areas when flies are resting there can be quite effective in reducing fly numbers.

In some cases, crops planted close to holding pens, especially corn, can also provide shade and should be treated with insecticides. If these fly resting areas can be located, treating them with residual sprays can be an important part of your fly control program.

Insecticides should be used on the day they are mixed because they will lose effectiveness over time. A general recommendation is to rotate insecticides; for example, use an organophosphate one time and on the next application rotate to a pyrethroid-based one.

Some residual insecticides will require removing animals from the buildings while the spray is applied. Also, some residual sprays have restrictions on treating the inside of buildings, treating animals under a certain age, or being used around lactating dairy animals. Always follow label instructions.

Biological control

A great deal of research has been directed toward biological control of the stable and the house fly, most of it with pteromalid wasps (Hymenoptera: Pteromalidae). These wasps are parasitic on dung-inhabiting fly pupae. The female wasp inserts its ovipositor into the pupal case of the fly and deposits one or more eggs. This action is termed a "sting". The wasp larvae feed on the developing fly and destroy it.

Several species of pteromalid wasps are produced and sold by commercial insectaries for control of feedlot filth flies; however, these species often are not native to the release area and winter survival is questionable. It is believed, however, that biological control can be effective if used as a part of a whole IPM program of sanitation, weed control, insecticides, etc.

Integrated pest management approach

The failure to bring about anything but a temporary reduction in fly populations has led researchers to believe that an integrated approach for control is the best way to combat the problem.

Good management and sanitation practices should be the first and most important component of an integrated approach of fly control for feedlots and dairies. Relying on insecticides or pteromalid wasps alone is temporary and costly. An integrated approach incorporates animal management, sanitation, manure management, facility design, biological control, and finally, judicious use of pesticides.

A good feedlot manager always plans ahead. When facilities are being built or expanded, good drainage and ease of manure management should be a major part of the plan. Areas where moisture accumulates within holding pens often become sites for fly breeding. The initial design and construction stage is the best time to eliminate these areas.

We have come a long way in understanding stable flies and house flies. Extensive research and study of these flies has given us new insight on how to deal with them. What is certainly clear is that a fly is not just a fly, and the method of controlling one species will not necessarily work on another.